Generally, a laser source includes a resonant cavity that contains an active laser medium. Stimulation of the active laser medium (or gain medium) is achieved by a pump beam emitted by a pump source. The pump beam enables a population inversion that is conducive to a stimulated emission generating the laser beam.
The compactness of a laser source is an important challenge when the said source is fitted in a device that has to remain compact. The size of the laser source can be a disadvantage when the device is portable.
Furthermore, when the device is subject to temperature variations, it is important that the laser source is not excessively affected by these variations. In the case of diode-pumped solid-state lasers, this last point is of critical importance considering that the central wavelength of laser diodes shifts by about 0.25 nm/° C. Depending on the profile of the absorption spectrum of the dopant ions under consideration, the energy of the laser can be affected.
For example, there are diode-pumped lasers called athermal lasers.
Generally, the principle of these sources is based on longitudinal pumping of doped amplifier bars. The pump is then guided in the bar, and the absorption length varies according to the operating temperature and the associated absorption coefficient.
Generally, the pump beam is emitted by a stack of diodes and collected by an optical device to be injected in the input of the amplifier bar.
For example, in the case of longitudinal pumping of a neodymium-doped yttrium aluminum garnet (Nd:YAG) crystal bar with a length of 80 mm, required for the absorption of at least 90% of the pump beam, the total length of the pumping and amplifier bar unit can reach 130 mm.
In this configuration, a significant part of the cavity length is governed by the size of the gain medium and the associated pump source generating the pump beam.
Although this type of solution is satisfactory, a more compact and efficient solution is preferable.